21309487 has 2 divisors, whose sum is σ = 21309488. Its totient is φ = 21309486.

The previous prime is 21309437. The next prime is 21309511. The reversal of 21309487 is 78490312.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21309487 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21309437) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10654743 + 10654744.

It is an arithmetic number, because the mean of its divisors is an integer number (10654744).

Almost surely, 2^21309487 is an apocalyptic number.

21309487 is a deficient number, since it is larger than the sum of its proper divisors (1).

21309487 is an equidigital number, since it uses as much as digits as its factorization.

21309487 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 12096, while the sum is 34.

The square root of 21309487 is about 4616.2199904251. The cubic root of 21309487 is about 277.2411329372.

Adding to 21309487 its reverse (78490312), we get a palindrome (99799799).

The spelling of 21309487 in words is "twenty-one million, three hundred nine thousand, four hundred eighty-seven".